I've just received a used 8566B and 80662A both listed as parts, but with good power supplies. The 8566B won't boot (error lights 1 and 2, which point to the uP board A15), and none of the 14 debugging LEDs light up on the CPU card (which the manual says should, and then blink out one by one). I followed the service manual steps to check the clocks on the 74HC112 dual negative edge JK flip-flops, both of which were fine. The manual then says to use heat and freezing spray to diagnose intermittent failures. I used my thermal camera, and the only warm chip was the PAL U20 (5180-2330). With my oscilloscope, I probed test pin bank No.1 (low, high, high, high, low, low, low, low, high) and then two ROMs and two SRAMs. Each one of them showed activity on the random pins I checked, and were repeating in a cycle that was 7 accesses long. With my limited knowledge, I think it appears that the CPU is stuck in a loop of some kind. Would the SRAMs, EPROMs, or the PAL be the most likely culprit? Or am I in the wrong place entirely? I have the "G" version ROM on the CPU board labelled 85660-60260 (which is a sticker over the original label of 85660-60182). Does anyone have any firmware (preferably G) that I can flash or verify against? And does anyone know how to place the 80662A display in the test pattern mode? I saw a handful of boards including the CPU sell for about $30-60 last week on ebay, which I am very sad I missed out on now, as it was before my SA arrived. The tools I have at my disposal at the moment are a DMM, variac, tek 2430 oscilloscope, arduinos, and two HP 16500 LAs with an array of cards. I would be willing to trade a 16500A with misaligned front floppy and 16510A card for a CPU board.